Why your engine idle is faulty

Qn: I have a Toyota Land Cruiser Prado TX Car - Engine 3RZ Petrol, which developed problems recently when it started giving a thick black smoke and my mechanic changed the airflow metre which I understand was old and needed replacement.

The thick black smoke stopped coming and even the sound stabilised to normal and the “check engine” light also went off but the car then developed high revs going to 2000 when there is no gear engaged but it goes to 1,100 when there is a gear. However, he told me to drive it like that for the revs “will eventually go down after two days.”

I have driven it for five days and they are still up. I have been told by the same mechanic who fixed the above that I need to change the throttle sensor/valve then it will stabilise. Sam Musoke Kasoma

Ans.Your Land Cruiser engine idle speed is faulty. A faulty engine idle is either too low or too high, either way, a vehicle will not run properly. A fuel injected petrol engine’s idle speed is controlled by the Idle Air Control (IAC) motor.

The engine idle speed is regulated when the IAC valve opens or closes a vacuum port. The malfunction of the IAC motor can be caused by one or a couple of factors. Before you replace the throttle position sensor or entire throttle body, ask your mechanics to re-inspect the engine for the following: a vacuum leak along the air intake line to the housing of the throttle body for a cracked or loose hose; the throttle body can accumulate carbon deposits or thin sludge (tar) which impede free movement of the throttle valve to allow flow of the air-fuel mixture.

Check the IAC motor operation when you turn ignition key on and off without starting to ensure the IAC valve moves in and out or does not have a leaking gasket. Check the positive crankcase ventilation (PCV) valve which evacuates engine crankcase vapours and incinerates them through the internal combustion system. The PCV valve should be inspected for free movement of its spring loaded plunger. Finally, your mechanics can carry out a computer diagnostic test to check operation of the oxygen sensors and coolant temperature sensors since you have replaced the mass air flow sensor.

Qn:Is there anything that I should know about a 2001 Audi A6 Quattro turbo fuel pump? I have replaced the pump and filter and I can smell petrol. Worried Dickson

Ans. If you have bought a quality replacement fuel pump and filter, the smell of petrol might be a result of leaking fuel hose connections to the fuel filter. Confirm that the hose clips are securely tightened and the fuel hose is not damaged. It is important to confirm that the seal under the screw type cover of the fuel pump housing on your fuel tank is not leaking. You will have to check under the rear passenger seat to access the fuel tank.

Qn:How often should I change the sparkplugs on my 2003 Volkswagen Bora 2.0cc? Henry KityoAns. The spark plug replacement interval on your Volkswagen depends on the type of spark plugs you use or the maintenance of your engine air filter and fuel system. If you have the high mileage iridium spark plugs then their lifespan is more than three years or 50,000 km. The ordinary but reputable spark plugs may be replaced after 15,000km, subject to inspection at every 5,000km service.

Qn: Why is my 1987 Toyota Camry slow to take off? It is hard to get from 0-20km/ph. JerryAns. Check or replace your engine serviceable parts such as the fuel filter, air cleaner, spark plugs and high tension leads. These affect the engine output as the combustion process requires a strong spark, clean air and unrestricted fuel supply.

Qn:I need advice on a foggy windshield of my Toyota Caldina. My windshield becomes foggy at night and have to either turn on the heater or clean it with say a cloth to clear. I guess, it is clear during the day because of the glass. Is there a possibility of blockage in the vents? Abdallah

Ans. The misting on your windshield happens on a cool or rainy morning or evening when the warm, moist air from your lungs meets the cold, moist air already in the car. The air from your lungs cools down and leaves the water vapour from your lungs with nowhere to go. The water vapour condenses on the nearest and coldest surface, which is the cold windscreen in front of you.

Your problem may not be the faulty or blocked air conditioning vents, rather it may be a correct procedure of using them. To solve this problem, you need to turn on your air conditioning with the selected warm temperature . Often this is uncomfortable if the air vents are directed to your face so you may switch it off early. Turn off the vents facing you and redirect the warm air to the vents below the windshield. Turning up high the air-conditioner for a little while and directing it through the windshield vents increases the air stream to the windshield and also evaporates the water condensed on your windshield faster.

Qn:My Mercedes Benz E320 engine won’t start.George Gumisiriza

Ans. You need to establish if the system check lights show on your instrument cluster do not fade when you try to start. This will be an indicator about the status of your car battery. Should the instrument cluster lights fade or not show at all, check whether your lights, horn or radio work. In case they do not, you need to check the battery condition or terminals for loose connection. Should your battery and connections be okay, then you will need to check the condition of your Mercedes key or drive authorisation function. You may need a qualified Mercedes technician and diagnostic computer assistance to interrogate your car’s electronic ignition system.

Qn: I have an E350 Mercedes 211. All of my data in the cluster system went out. A few days later, the automatic locks would not self-lock. A few days later I got nothing. I charged my battery and got a little something. Can you help me? Worried reader